DYNAMIC SURFACE-TENSION MEASUREMENTS AND L-S-RATIO IN AMNIOTIC-FLUID BEFORE BIRTH IN COMPARISON WITH THE RESPIRATORY COMPLIANCE OF THE NEWBORNS IMMEDIATELY AFTER PARTURITION

Abstract

In 65 pregnant women between 27th and 42nd gestational week amniotic fluid was collected on average of 4.2 h before birth and its amount of surfactant determined by dynamic surface tension measurement in the Wilhelmy balance and the L/S [lecithin-sphinogomyelin] ratio. These values were compared to the respiratory compliance of the newborns after birth. Respiratory compliance was measured by the airway occlusion technique. Measurement of dynamic surface tension allowed prediction of lung maturity and the incidence of RDS [respiratory distress syndrome]. A quantitative relationship was described between the surface tension of the amniotic fluid and the surface tension of the lungs in form of the respiratory compliance. The surface tension, measured by the Wilhelmy balance, was better correlated (r = 0.85) than the L/S ratio (r = 0.58) with the respiratory compliance of the newborns. The surface tension measurement allows a better prediction of the severity of the RDS than the determination of the L/S ratio. This can be explained by the fact that the surface tension measurement in the amniotic fluid represents the total effect of SAM (surface active material) while the L/S ratio represents only about 60% of SAM. The L/S ratio gave a better correlation to the general maturity of the fetus than the surface tension. The L/S ratio is partially influenced by the lung maturity and partially by gestational age of the fetus.